For example, Patent Documents 1 and 2 disclose conventional vortex generator devices each including a butterfly valve, which is in a plate shape and rotated in a passage through which intake air flows. The conventional vortex generator device causes the butterfly valve to rotate to throttle intake airflow and to concentrate the intake airflow toward a specific periphery in a cross section of the passage. Such a conventional vortex generator device is conceived not to cause a flow other than a concentrated flow, which is concentrated to the specific periphery, thereby to restrict the concentrated flow from decreasing in flow velocity and to restrict the concentrated flow from diffusing.
When the butterfly valve is at the full-close angle, the butterfly valve throttles intake airflow most to concentrate the intake airflow toward the specific periphery. In addition, when the butterfly valve is at the full-close angle, a clearance (full-close CL) is formed between the perimeter of the butterfly valve and a passage wall of the passage other than the specific periphery of the passage. In order not to cause a flow other than the concentrated flow, the clearance (full-close CL) is required to be substantially zero, as much as possible, when the butterfly valve is at the full-close angle. It is further noted that, in order to reduce the clearance (full-close CL) to substantially zero as much as possible, it is required to employ an elastic material to form the perimeter of the valve element or it is required to enhance accuracy of components. Consequently, manufacturing cost for the valve element and/or the components may increase.
In Patent Document 2, a partition plate is equipped on the downstream side relative to a rotation locus of the butterfly valve, thereby to restrict the concentrated flow from diffusing. Nevertheless, even the configuration of Patent Document 2 may still generate a flow other than the concentrated flow. Consequently, in the configuration of Patent Document 2, a flow velocity of the concentrated flow may decrease, and a vortex may not be generated desirably.
(Patent Document 1)
Publication of Unexamined Japanese Patent Application No. 2001-248450
(Patent Document 2)
Publication of Unexamined Japanese Patent Application No. 2010-190166